The present invention relates generally to a power steering system for a motor vehicle, and more particularly, to its improvement in a connection between a gear housing for accommodating a steering-force transmitting gear and a cylinder sleeve of a assisting power cylinder.
As disclosed in JP-U 6-22156, a typical power steering system for a motor vehicle comprises a cylinder sleeve of a power cylinder connected to a gear housing for accommodating a steering-force transmitting gear such as a rack-and-pinion.
In the power steering system, a cylindrical wall and a butt wall substantially orthogonal thereto are provided to a connection of the gear housing with the power cylinder. The cylinder sleeve is engaged on the outer periphery of the cylindrical wall to have a front-end face abutting on the butt wall. At an engagement of the cylinder wall and the cylinder sleeve, a connecting corner between the cylindrical wall and the butt wall often undergoes stress in a concentrated way, and is thus formed to have an R-shape as large as possible.
With the typical power steering system, however, due to the cylinder sleeve being thin, the R-shape of the connecting corner cannot be formed with sufficiently large radius of curvature, raising a problem of limited relief of stress concentration.
Specifically, favorable achievement of the positioning accuracy of the cylinder sleeve with respect to the gear housing needs plane butt of the front-end face of the cylinder wall on the butt wall. However, with increasing radius of curvature of the R-shape on the gear-housing side, a flat portion of the front-end face of the cylinder sleeve should be narrowed. Thus, due to adjustment between the two requirements, the typical power steering system is restricted in increase in the radius of curvature of the R-shape.